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In order for the export to be functional, the exportLocation and exportACL properties must be set for the relevant application's <Sessions> element. In addition, the <SessionCache> element must either omit, or turn on the cacheAssertions property. It defaults on, but may be explicitly turned off to optimize the cache when assertions don't need to be accessed later.
Then, when instructed to do so for a request (via the exportAssertion content setting), the application will be given a header or variable called Shib-Assertion-Count with the number of assertions that are available.
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